Expandable TFE Copolymers, Method of Making, and Porous, Expanded Articles Thereof

ABSTRACT

A true tetrafluoroethylene (TFE) copolymer of the fine powder type is provided, wherein the copolymer contains polymerized comonomer units of at least one comonomer other than TFE in concentrations of at least or exceeding 1.0 weight percent, and which can exceed 5.0 weight percent, wherein the copolymer is expandable, that is, the copolymer may be expanded to produce strong, useful, expanded TFE copolymeric articles having a microstructure of nodes interconnected by fibrils. Articles made from the expandable copolymer may include tapes, membranes, films, fibers, and are suitable in a variety of end applications, including medical devices.

BACKGROUND OF THE INVENTION

The invention relates to fluorocopolymers, as defined herein to denoteany fluoropolymer containing tetrafluoroethylene monomer units and atleast or more than 1.0% by weight of units of at least one othercomonomer,* polymerized to produce an expandable tetrafluoroethylenecopolymer of the fine powder type. A process of polymerization of thesemonomers is described, as well as the porous products produced byexpansion (stretching under controlled conditions) of the aforesaidcopolymers. * See, e.g., Fluoroplastics—Vol 1: Non-Melt ProcessibleFluoroplastics; Williams Andrew, Inc., Norwich, N.Y., at p. 25 19(2000); see, also, ISO 12086.

Techniques for the dispersion polymerization of tetrafluoroethylene(TFE) monomer are known. Dispersion polymerization of TFE produces aresin that has come to be known as “fine powder”. See, e.g., U.S. Pat.No. 4,016,345 (Holmes, 1977). In such processes, generally, sufficientdispersing agent is introduced into a water carrier such that, uponaddition of tetrafluoroethylene monomer in the presence of a suitablepolymerization initiator and, upon agitation and under autogenoustetrafluoroethylene pressure of 10 to 40 kg/cm², the polymerizationproceeds until the level of colloidally dispersed polymer particles isreached and the reaction is then stopped.

In contrast, particulate tetrafluoroethylene resins have also beenproduced by a process of suspension polymerization whereintetrafluoroethylene monomer is polymerized in a highly agitated aqueoussuspension in which little or no dispersing agent is employed. The typeof particles produced in suspension polymerization has been termed“granular” resin or “granular powder”. See, e.g., U.S. Pat. No.3,655,611 (Mueller, 1972).

For both polymerization processes, copolymerization oftetrafluoroethylene with various fluorinated alkyl ethylene comonomershas been described. See, for example, U.S. Pat. No. 4,792,594 (Gangal,et al., 1988). However, the present invention relates, to specifically,to the aqueous dispersion polymerization technique, in which the productof the polymerization reaction is the copolymer of the inventiondispersed within an aqueous colloidal dispersion. In this process,tetrafluoroethylene monomer is pressured into an autoclave containingwater and polymerization initiators, along with paraffin wax to suppresscoagulum formation and an emulsifying agent. The reaction mixture isagitated and the polymerization is carried out at suitable temperaturesand pressures. Polymerization results in the formation of an aqueousdispersion of polymer particles, and the dispersed polymer particles maysubsequently be coagulated by techniques known in the art to obtain whathas become known as the fine powder form of the polymer.

Various prior patents have disclosed techniques for thehomopolymerization of tetrafluoroethylene and for the polymerization ofTFE with small amounts (<1.0% by weight) of other monomers. Among thoseare included U.S. Pat. No. 4,576,869 (Malhotra, 1986) and U.S. Pat. No.6,177,533B1 (Jones, 2001).

Fine powder resins are known to be useful in paste extrusion processesand in stretching (expansion) processes in which the paste-extrudedextrudate, after removal of extrusion aid lubricant, is stretched toproduce porous, strong products of various cross-sectional shapes suchas rods, filaments, sheets, tubes, etc. Such a stretching process isdisclosed in the pioneering U.S. Pat. No. 3,953,566 (Gore, 1976),assigned commonly with the instant invention.

The expansion process as it applies to fluorocarbon polymers is fullydescribed in the aforesaid '566 patent, and that process has come toidentify what is currently termed the “expanded” form of TFEfluoropolymers, and will serve to define what is meant herein as anexpanded or expandable TFE polymer or copolymer.

The term “copolymer” as it has been used in connection withfluoropolymers in the prior art has been inconsistently applied. For allpurposes herein, as set out in the Fluoroplastics text cited above andin the ISO 12086 classification cited above, the normal convention ofpolymer science will be followed, and the term “copolymer” will apply toany fluoropolymer containing more than 1.0% by weight of at least onecomonomer in addition to TFE. A fluoropolymer containing less than 1.0%comonomer is properly categorized as a “modified” homopolymer (Id.),although the term “copolymer” has been misapplied in the literature whenreferring, in fact, to “modified” homopolymers. One must examine eachparticular instance of such use to determine the actual concentrationsof comonomers employed to determine whether, in fact, the referencedcomposition is a “modified” homopolymer or a true copolymer, that is,whether or not the polymeric product, in fact, contains more than 1.0weight percent comonomeric units.

By definition herein, the invention provides a true TFE copolymer, ofthe fine powder type, that is expandable, as defined above, to produceuseful, expanded TFE copolymeric products.

U.S. Pat. No. 4,837,267 (Malhotra, 1989) discloses a three-componentcomposition termed “core-shell TFE copolymers”, which are described asnon-melt processable, including chlorotrifluoroethylene (CTFE) monomerresiding in the core and having recurring units of a comonomer ofperfluoro(n-alkylvinyl) ether of 3-7 carbon atoms (col. 1, lines 45-55).The total comonomer content in the particles is said to be between 0.001and 2 weight percent. The examples presented all relate to terpolymershaving comonomeric concentrations much less than the range described,namely 0.23% CTFE and 0.0145% PPVE (total of 0.2445 wt %) in Example 1,and 0.13% HFP and a minute, undeterminable amount of PPVE in Example 2.The stated upper limit of 2% is therefore unsupported by thespecification and examples presented. Moreover, there is no disclosureor suggestion in the '267 patent of an expanded or an expandable TFEcopolymeric composition.

Japanese Patent Application (Kokai) 2005-306033A, published Nov. 4,2005, discloses thin films of PTFE which are said to be non-porous,non-gas-permeable (p. 5), and to contain “trace monomer units” in therange of 0.001-2 mol % (p. 7) described as “modified” PTFE. Theobjective of the invention is said to be obtained by “heat treatment” of“porous PTFE resin film” to render the film “substantially nonporous”.There is no disclosure or suggestion in this reference of a porous,expandable TFE copolymeric composition.

U.S. Pat. No. 4,391,940 (Hoechst, 1983) discloses and describes apartially modified tetrafluoroethylene polymer having a “three-shell”particle structure. The resins are said to be suitable for pasteextrusion to produce cable insulation and highly stretchable, unsinteredtapes (940 patent, Abstract). This patent describes fluorinatedmodifying monomers which are capable of copolymerizing withtetrafluoroethylene, such as perfluoropropene, perfluoroalkyl vinylether, and halogen-substituted or hydrogen-substituted fluoroolefins.The specification cautions that the total amount of the comonomermodifying agent should be so low that the specific properties of thepure polytetrafluoroethylene are retained, that is, there remains nopossibility of processing from the melt because of the extremely highmelt viscosity for such modified polymers. (940 patent, col. 1, I. 62 etseq.) Products disclosed include modified polymer particles having acore of a polymer of “0.05 to 6% by weight” of at least one modifyingfluoroolefin comonomer, a first, inner shell, immediately adjacent thecore, of TFE units, and a second, outer shell, immediately adjacent theinner shell, of a polymer comprising “0.1 to 15% by weight” of units ofat least one modifying fluoroolefin (col. 3, I. 5, et seq.). Examples ofthe “three-shell” products provided in this reference for illustrationof the principles disclosed therein show that tapes, upon stretching,after removal of lubricant, developed defects or tore completely atrelatively modest stretch ratios. For example, the detailed proceduredescribed in EXAMPLE 31, at col. 14, I. 60 to col. 16, I. 6, produced aproduct which developed defects at a 4:1 stretch ratio and torecompletely at a stretch ratio of 8:1 (940 patent, Table III).

For comparison and to place various of the prior art disclosures incontext, recently issued U.S. Pat. No. 6,841,594 (Jones, 2005) instructsthat polytetrafluoroethylene (PTFE) refers to the polymerizedtetrafluoroethylene by itself without any significant comonomer present,and that “modified” PTFE refers to TFE polymers having such smallconcentrations of comonomer that the melting point of the resultantpolymer is not substantially reduced below that of PTFE. Theconcentration of such comonomer, consistent with prior citations above,is preferably less than 1 weight %, more preferably less than 0.5 weight%. The modifying comonomers cited include, for example,hexafluoropropylene (HFP), perfluoro(methyl vinyl ether) (PMVE),perfluoro (propyl vinyl ether) (PPVE), perfluoro (ethyl vinyl ether)(PEVE), chlorotrifluoroethylene (CTFE), perfluoro-butyl ethylene (PFBE),or other monomer that introduces side groups into the molecule. Theseinstructions are consistent with the disclosures above and with thedefinitions contained herein, i.e., that the term “copolymer”, ascontrasted with the term “modified homopolymer”, shall mean anyfluoropolymer containing more than 1.0% by weight of at least onecomonomer in addition to TFE.

U.S. Pat. No. 6,127,486 (Burger, et. al., 2000) discloses a blend of afluoropolymer and a “thermoplastic”, wherein the “thermoplastic” is saidto include a “PTFE copolymer” (col. 4, I. 46). The specificationinstructs that, for the resins described therein, the amount ofcomonomer is limited such that the [modified] PTFE exhibits propertiesof “not being processable in the melt.” (Emphasis in original). The PTFEis referred to as modified PTFE “in which the comonomers are containedin an amount below 2, preferably 1 wt. % in PTFE.” (Col. 4, I. 50) Noexamples are provided of any copolymer having greater than 1.0 weight %of an additional comonomer, and the patent concerns blends of polymers,a different physical form entirely from the true copolymers which formthe subject matter of the present invention.

Another recent reference, Japanese Patent Application No. 10-243976(Asahi Glass Co., Ltd., claiming priority to Dec. 26, 1997) is stillfurther instructive of the state of the art in the field of copolymersand modified homopolymers of TFE. That patent application, titled“Tetrafluoroethylene Copolymer and Application Thereof”, contains claimsto polymers having, inter alia, additional comonomer content in therange of 0.005 to 0.05 mol % (about 0.012 to 0.123 wt %). The patentdiscusses known copolymerization techniques and discloses that afurther, related Japanese application, JP (Kokoku) 3-66926, proposes amethod for modifying PTFE by employing R_(f)—CH═CH₂ (where R_(f) is a_(C1-10) perfluoroalkyl group) as a comonomer. In the proposed method,the comonomer is continuously added during the polymerization process inorder to enhance modification in the initial period. The modification issaid to be primarily performed in order to improve the pasteextrudability of fine powders, for example, to reduce extrusionpressure, and the content of polymerization units based on comonomers,while less than 0.5 wt %, is “still comparatively high in substantialterms” (0.1 wt % or higher). Consequently, the product has substantiallyno melt moldability and possesses markedly reduced crystallinity. Thereference describes “another drawback”, that such modified PTFE becomesless heat resistant because of the structure of the comonomersintroduced. Finally, the Asahi patent application concludes, quotingtherefrom:

-   -   In addition, the comonomer structure impairs molecular        orientation, causing breakage during stretching and making the        product substantially unusable for the manufacture of stretched        porous articles.    -   An object of the present invention is to provide a PTFE product        that has excellent extrudability, can be uniformly stretched,        and yields high-strength porous articles.

This objective is then said to be obtained by limiting the introductionof polymerization units based on comonomers copolymerizable with TFE toan amount that has no discernible effect on processability.

Specifically, the Asahi application provides a product of TFE and afluorinated comonomer expressed by the general formula CH₂═CH—R_(f)(where R_(f) is a C₁₋₁₀ perfluoroalkyl group, wherein this polymercontains 0.005 to 0.05 mol % polymerization units based on thefluorinated comonomer. Further, a porous polymer article is provided,obtained by a process in which a powder composed of the aforementionedmodified PTFE is paste-extruded and then stretched at a temperature of250° C. or higher. This reference, however, specifically cautionsagainst polymerization in which the amount of copolymerized monomerexceeds certain limits. The application states, again quoting directly:

-   -   The content of the polymerization units based on fluorinated        comonomer in the present invention must be rigorously controlled        because of considerations related to stretchability. The content        of the units in the PTFE must fall within a range of 0.005 to        0.05 mol %. A content above 0.05 mol % brings about a slight        reduction in polymer crystallinity, results in a lower paste        extrusion pressure, and has a markedly adverse effect on        stretchability. A content below 0.005 mol % makes it        substantially more difficult to improve the physical properties        of a stretched article or to obtain other modification effects.        A range of 0.01 to 0.04 mol % is particularly preferred.

This, again, is consistent with the other teachings of the prior artreferences discussed hereinabove. In Example 4 of this Asahi reference,in which a “high” content (by applicant's definition), 0.42 wt %, ofperfluorobutylethylene comonomer was employed, the paste extrusionpressure was desirably low, and “excellent” extrudability was obtained.However, a test specimen, on stretching, broke. The specificationdiscloses, at this “high” level of comonomer concentration of 0.42 wt %,“ . . . breakage occurred during stretching, and it was impossible toobtain a porous article.” (p. 12, §0050). In spite of these cautionaryteachings, and in contrast thereto, the present invention is directed totrue TFE copolymers, all containing in excess of 1.0 weight percentcomonomer units, all of which are expandable to form porous expandedarticles, to a process for their manufacture, and to the expandedarticles produced thereby. No known prior art reference discloses orsuggests such porous, expanded copolymeric articles or the resins fromwhich they are produced.

It is wholly unexpected, and contrary to prior art teachings, that a TFEcopolymer, having comonomeric unit concentrations in the high rangesclaimed herein, can be expanded as disclosed hereinbelow, to and beyonda 25:1 stretch ratio, to form a uniform, viable shaped article. Thissynergistic result is truly surprising to one skilled in this art.

SUMMARY OF THE INVENTION

A process is provided for the copolymerization of an expandabletetrafluoroethylene (TFE) copolymer of the fine powder type, thecopolymer containing 99.0% or less by weight tetrafluoroethylene (TFE)monomer units and at least, or greater than, 1.0% by weight, of units ofat least one other comonomer, that is, other than tetrafluoroethylene.The other comonomer is an ethylenically unsaturated comonomer having asufficiently high reactivity ratio to TFE to enable polymerizationtherewith. The process includes the steps of copolymerizing the TFEmonomer and the at least one other monomer in a pressurized reactor byfeeding 99.0% or less by weight of the TFE monomer into the reactor,feeding at least or greater than 1.0% by weight of the other comonomerinto the pressurized reactor, wherein percentages are based upon totalweight of monomers fed, initiating polymerization of the monomers with afree radical initiator, and stopping the feeding of the other monomer ata point in time in the polymerization reaction prior to completion ofthe reaction. In one embodiment, optionally, excess comonomer is removed(evacuated) from the reactor, as needed, prior to completion of thereaction. The at least one other comonomer may be an olefin such asethylene, propylene or isobutylene, a fluorinated monomer selected fromthe group consisting of chlorotrifluoroethylene (CTFE),hexafluoropropylene (HFP), vinylidene fluoride (CFH═CH₂), vinylidenedifluoride (CF₂═CH₂), hexafluoroisobutylene (HFIB) andtrifluoro-ethylene (CF₂═CFH), a fluorodioxole of the general formula:

wherein R₁ and R₂═F or a 1-3 carbon alkyl group containing at least onefluorine, and X, Y may be F 10 and/or H;a fluorodioxole of the general formula:

wherein R_(f) is a perfluoroalkyl carbon of 1-5 atoms, and R₁, R₂ may beF and/or CF₃; and

a fluorodioxalane of the general formula:

wherein R₁, R₂ may be F and/or a perfluoroalkyl carbon of 1-5 atoms.Alternatively, the at least one other comonomer may be a perfluoroalkylethylene monomer such as a monomer selected from the groupperfluorobutylethylene (PFBE), perfluorohexylethylene (PFHE) andperfluoro-octylethylene (PFOE), or it may be a perfluoroalkyl vinylether monomer such as a monomer selected from the group consisting ofperfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether)(PEVE), and perfluoro(propyl vinyl ether) (PPVE). More than one othercomonomer may be fed into the pressurized reactor, to producemulticomponent copolymers, i.e., terpolymers, etc.

The monomer feeds may be introduced as a precharge in thepolymerization, or the at least one other comonomer may be introducedincrementally or intermittently during the reaction.

The process in one embodiment preferably includes stopping the feedingof the at least one other comonomer at less than 90% of the reactioncompletion.

Higher concentrations of comonomer in the copolymer produced areachieved by feeding the at least one other comonomer at higherconcentration levels, such as at least 1.5% by weight, at least 2.0% byweight, and exceeding 5.0% by weight of the at least one other comonomerto the reactor.

The aforesaid process produces an expandable tetrafluoroethylene (TFE)copolymer of the fine powder type containing 99.0% or less by weight ofpolymerized tetrafluoroethylene (TFE) monomer units and at least, orgreater than, 1.0% by weight, of polymerized comonomer units of the atleast one other comonomer fed into the reaction, based on total weightof polymer produced. This true copolymer is expandable to a porous,expanded copolymeric material having a microstructure characterized bynodes 1 interconnected by fibrils 2, as shown in FIG. 1, described morefully below. Further views of alternative unique node, 1, and fibril, 2,microstructures are shown in FIGS. 2 and 3.

The expandable copolymer produced contains at least one otherpolymerized comonomer within the following group: olefins such asethylene, propylene and isobutylene; fluorinated comonomers such aschlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), vinylidenefluoride (CFH═CH₂), vinylidene difluoride (CF₂═CH₂),hexafluoroisobutylene (HFIB), trifluoroethylene (CF₂═CFH),fluorodioxoles and fluorodioxalanes; and perfluoroalkyl ethylenemonomers, including perfluorobutylethylene (PFBE),perfluorohexylethylene (PFHE) and perfluorooctylethylene (PFOE), and aperfluoroalkyl vinyl ether monomer, including perfluoro(methyl vinylether) (PMVE), perfluoro(ethyl vinyl ether) (PEVE), and perfluoro(propylvinyl ether) (PPVE). The copolymer produced may include more than oneother polymerized comonomer, and the comonomer content in the copolymeralways exceeds 1.0% by weight, may exceed 1.5% by weight polymerizedunits of the other comonomer and, indeed, may exceed 5.0 weight % ofpolymerized units of the other comonomer(s).

In a further embodiment of the invention, copolymer materials areproduced which exhibit unique adhesion characteristics which cannot beachieved in PTFE homopolymers. That is, the copolymer can be adhered toitself or other materials after subjecting it to lower temperatureand/or shorter time and/or lower pressure than what is required foradhering PTFE homopolymer to itself. For example, as described laterherein with respect to room temperature adhesion testing, this adhesion,or bonding, can be achieved at temperatures at or below about 290° C.with these unique copolymers (hence, at lower temperatures than requiredfor PTFE homopolymers).

The copolymer of the invention is produced in the form of fine particlesdispersed within an aqueous medium which may be coagulated using knowntechniques to produce fine powder resins. Porous, expanded TFE copolymermaterials having a microstructure of nodes interconnected by fibrils arefurther provided according to the invention. These porous, expandedcopolymeric materials can be produced in the form of shaped articlessuch as sheets or films, tubes, rods, and continuous filaments, andthese articles are generally strong, that is, their matrix tensilestrengths in at least one direction exceed 5,000 psi. Matrix tensilestrengths in at least one direction can, for certain products, exceed30,000 psi, thus providing extremely strong, porous, true copolymericexpanded TFE articles useful in many applications.

The copolymer of the invention is produced in the form of fine particlesdispersed within an aqueous medium which may be coagulated using knowntechniques to produce fine powder resins. Porous, expanded TFE copolymermaterials having a microstructure of nodes interconnected by fibrils arefurther provided according to the invention. These porous, expandedcopolymeric materials can be produced in the form of shaped articlessuch as sheets or films, tubes, rods, and continuous filaments, andthese articles are generally strong, that is, their matrix tensilestrengths in at least one direction exceed 5,000 psi. Matrix tensilestrengths in at least one direction can, for certain products, exceed30,000 psi., thus providing extremely strong, porous, true copolymericexpanded TFE articles useful in many applications. In a furtherembodiment, such expanded TFE materials may be compressed or otherwiseprocessed to achieve a reduction in porosity utilizing processingtechniques known in the art.

The copolymer of the present invention can be used in a wide variety ofmedical and commercial devices. Medical devices include theincorporation of the inventive copolymer into long and short termimplantable devices, as well as in disposable, or single use, suppliesand devices. These devices include, but are not limited to, vasculargrafts (to repair, replace, bypass or augment a blood vessel or anothervascular graft), other shunting conduits, surgical and laparoscopicsheets and patches, endoluminal prostheses (e.g., stent-grafts),components of cell containment devices, and substrates for drugdelivery, catheters, space filling or augmentation devices, jointspacers, surface coatings for devices, lenses, work surface or cleanroom surface coatings, seals, gaskets, blood contact surfaces, bags,containers and fabric liners.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1, is a SEM photomicrograph of an expanded sheet of a copolymericresin produced according the invention herein, taken at 200×magnification, showing the node 1 and fibril 2 microstructure of thismaterial, the respective nodal intersections being interconnected by themultiplicity of fibrils 2;

FIG. 2 is a SEM photomicrograph of the expanded beading specimen of thecopolymeric resin produced in Example 6, taken at 200× magnification,showing the node 1 and fibril 2 microstructure of this material, therespective nodal intersections being interconnected by the multiplicityof fibrils 2;

FIG. 3 is another SEM photomicrograph of the expanded sheet specimen ofthe copolymeric resin produced in Example 6, taken at 20,000×magnification, showing a node 1 and fibril 2 microstructure; and

FIG. 4 includes differential scanning calorimetry (DSC) scans showingthe melt transition temperature peaks of the materials of Examples 10,12 and 13, as well as that of a comparative PTFE homopolymer.

DESCRIPTION OF THE INVENTION

A process for the polymerization of a true tetrafluoroethylene (TFE)copolymer of the fine powder type is provided, wherein the copolymercontains polymerized comonomer units of at least one comonomer otherthan TFE in concentrations of at least or exceeding 1.0 weight percent,and which can exceed 5.0 weight percent, wherein the copolymer isexpandable, that is, the copolymer may be expanded to produce strong,useful, expanded TFE copolymeric articles having a microstructure ofnodes interconnected by fibrils.

The copolymer of this invention is produced by a polymerization processwherein the copolymerization reaction is started by a suitableinitiator, after which initiator addition is stopped, allowing thereaction to slow down and proceed to completion, at a point between 15%and 90% of the progression of the reaction toward completion. Preferablythe initiator addition is stopped at about the mid-point of thereaction, i.e., at 20-60% to completion.

Substantially non-telogenic dispersing agents are used. Ammoniumperfluoro octanoic acid (APFO or “C-8”) is one acceptable dispersingagent. Programmed addition (precharge and pumping) is known and ispreferred. Attention must be paid to ingredient purity to achieve thedesired properties in polymerizations as described herein. Ionicimpurities, which can increase ionic strength, in addition to solubleorganic impurities, which can cause chain transfer or termination, mustbe minimized. It is clearly important to employ ultra pure water in allsuch polymerization reactions.

The break strength associated with an extruded and expanded (stretched)TFE polymeric beading produced from a particular resin is directlyrelated to that resin's general suitability for expansion, and variousmethods have been employed to measure break strength. The followingprocedure was used to produce and test expanded beading specimens madefrom the copolymers of this invention, the data for which are reportedhereinbelow.

For a given resin, 113.4 g of fine powder resin is blended together with130 cc/lb (24.5 g) of Isopar® K. The blend is aged for about 2 hours at22° C. in a constant temperature water bath. A 1-in. diametercylindrical preform is made by applying about 270 psig of preformingpressure for about 20 seconds. The preform is inspected to ensure it iscrack free. An extruded beading is produced by extruding the preformed,lubricated resin through a 0.100 in. diameter die having a 30 degreeincluded inlet angle. The extruder barrel is 1-in, in diameter and theram rate of movement is 20 in./min. The extruder barrel and die are atroom temperature, maintained at 23° C., plus or minus 1.5° C. The IsoparK is removed from the beading by drying it for about 25 to minutes at225-230° C. Approximately the first and last 8 ft. of the extrudedbeading are discarded to eliminate end effects. A 2.0 in. section of theextruded beading is expanded by stretching at 290° C. to a final lengthof 50 in. (expansion ratio of 25:1) and at an initial rate of stretch of100% per second, which is a constant rate of 2 in. per second.Approximately a 1 ft. length from near the center of the expandedbeading is removed, and the maximum break load of the removed sampleheld at room temperature (23° C. plus or minus 1.5° C.) is measuredusing an Instron® tensile tester using an initial sample length of 2 inand a crosshead speed of 12 in/min. Measurements in duplicate areobtained and reported as the average value for the two samples. Thisprocedure is similar to that described in U.S. Pat. No. 6,177,533B1, Theexpansion here is carried out at 290° C. instead of 300° C.

Core-shell resin structures containing polymerized monomers additionalto TFE, structurally similar to those produced by the techniquesdescribed herein, and as described earlier herein, have been known forsome time. See, e.g., U.S. Pat. No. 4,576,869 (Malhotra), U.S. Pat. No.6,541,589B1 (Baillie) and U.S. Pat. No. 6,841,594B2 (Jones). In theexamples which follow, and for the claimed compositions, the resinsproduced according to the present invention are all true copolymers,i.e., comonomer content exceeding 1.0 weight percent, verified usingsolid state NMR spectroscopy, as well as mass balance and detection ofresidual monomer in the gas phase of the polymerization batch, throughgas chromatography. The compositions are all expandable to a stretchratio of at least 25:1, to form expanded copolymeric articles havingtheir unique node, 1, and fibril, 2, microstructure as shown in FIG. 1,verifiable through SEM examination, as demonstrated below. Further viewsof alternative unique node, 1, and fibril, 2, microstructures are shownin FIGS. 2 and 3.

Characterization of copolymer materials can be performed via standardanalytical techniques available in the art including, but not limitedto, DCS, NMR (including fluorine, proton, carbon and other known NMRtechniques), TGA, IR, FTIR, Raman spectroscopy, and other suitabletechniques.

Tests Differential Scanning Calorimetry (DSC)

This test was performed using a TA Instruments Q2000 DSC and TAInstruments standard aluminum pans and lids for Differential Scanningcalorimetry (DSC). Weight measurements were performed on a Sartorius MC210P microbalance.

Calibration of the Q2000 was performed by utilizing the CalibrationWizard available through the Thermal Advantage software supplied withthe device. All calibration and resulting scans were performed under aconstant nitrogen flow of 50 ml/min.

The sample was loaded info the pan and the weight was recorded to 0.01mg precision, with samples ranging from 5.00 mg to 10.00 mg. Thesevalues were entered into the Thermal Advantage control software for theQ2000. The lid was placed on the pan and crimped using a standard press.A similar pan for reference was prepared, with the exception of thesample article, and its weight was also entered into the software. Thepan containing the sample article was loaded onto the sample sensor inthe Q2000 and the empty pan was loaded onto the reference sensor. Thesamples were then equilibrated at −50° C. and ramped at 20° C./min to400° C. Data were analyzed using Universal Analysis 2000 v.3.9A from TAInstruments.

Adhesion Testing

Extruded PTFE tapes were cut into rectangles with dimensions of 20 mmwidth×75 mm length and were thermally bonded in a Carver press model#3895, from Fred S. Carver Inc, Wabash, Ind. to aluminum foil substratesto create 90 degree peel samples. The tapes were bonded to 23 micronthick Heavy Strength aluminum foil from Reynolds Consumer Products Co,Richmond, Va. 23230. Polyimide release film, Upilex grade 25SDADB, 25microns thick, available from UBE Industries, LTD., Tokyo, Japan wasused to prevent adhesion to the press plates and provide a pre-crack toinitiate peel during 90 degree peel testing. Melt press time, and normalforce were 30 minutes and 450 Kg. Samples were prepared at melt presstemperatures of 195° C., 290° C., and 350° C. Once bonded the sampleswere cooled while still under pressure to approximately 21° C. forapproximately 20 minutes. Foil-PTFE tape peel samples at each bondingtemperature were prepared simultaneously to maintain a common thermalhistory. A 90 degree peel test is conducted at a test speed of 1 mm/secusing an Imass SP-2000 Slip-Peel Tester, available from InstrumentorsInc., Strongsville, Ohio. Results were reported in J/m², and anymeasurable value defined that the material exhibits adhesion. Forsamples where the sample fell apart prior to testing, a “no adhesion”value was reported.

NMR Analysis

A sample of 10 to 25 mg was packed into a 2.5 mm ZrO spinner usingstandard Bruker 2.5 mm packing accessories (Bruker BioSpin Inc., Boston,Mass.). ¹⁹F spectra were collected at about 296 Kelvin on aBruker-BioSpin 2.5 mm cross polarization magic angle spinning (CPMAS)probe positioned in a standard bore 7.05 T Bruker ultra shieldedsuperconducting magnet. The samples were positioned at the magic angleand spun at 32.5 kHz. A Bruker BioSpin Avance II 300 MHz system was usedto collect ¹⁹F NMR data at 282.4 MHz. Software used for data acquisitionand data processing was Topspin 1.3. The data was collected using theconditions specified in Table B. The spectra were externally referencedto PTFE at −123 ppm.

Table A NMR Instrument Used

TABLE A NMR Instrument Used Manufacturer Bruker BioSpin Model Avance II300 MHz Magnet 7.05 T Ultrashielded Probe Bruker 2.5 mm CPMASMultinuclear Rotor Standard Bruker 2.5 mm ¹⁹F Frequency 282.4 MHzSoftware Topspin 1.3

TABLE B NMR Acquisition Parameters Parameter Value MAS Spinning speed32.5 kHz Pulse length (11°) 0.4 □s Spectral Window 113636 Hz (402 PPM)Transmitter offset −100 PPM Number of scans 2000 Recycle delay 3 sAcquisition Time 150 ms Acquired Data Points used in Fourier 8000Transform Zero Fill before Fourier Transform 32 k Line broadening 15 HzThe following examples are intended to be illustrative of the invention,but are not to be construed as limiting the scope of the invention inany way.

EXAMPLE 1

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water,18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic aciddissolved in about 50 g of DI water. The reactor and contents wereheated above the melting point of the wax. The reactor was repeatedlyevacuated and pressurized (to about 1 Atm or less) with TFE until theoxygen level was reduced to 20 ppm or less. The contents were brieflyagitated at about 60 rpm between evacuation and purge cycles to ensurethat the water was deoxygenated.

The reactor was heated to 83 C and agitated at 60 rpm. Subsequently, 0.8MPa of VDF was added followed by addition of TFE until the pressurereached 2.8 MPa. At this time, KMNO4 in a DI water solution (0.063 g/L)was injected at 80 mL/min until approximately 2 kg of TFE was added.After addition of the 2nd Kg of TFE, the pressure in the reactor wasreduced to 50 Kpa using vacuum and pressurized with fresh TFE to 2.8MPa. The KMnO4 was added at 20 mL/min for the 3rd Kg of TFE and furtherreduced to 10 mL/min for the 4th Kg of TFE. After the 4th Kg of TFE wasadded, KMnO4 was no longer added.

Approximately 320 g of 20% APFO solution was added in 40 mL increments,the first increment being added after about 1 Kg of TFE had been added,followed by increments after each additional Kg of TFE, so that thefinal increment was added after 8 Kg of TFE had been reacted.

The polymerization reaction was then allowed to continue and thereaction stopped after 14.3 Kg of TFE had been added to the reactor. Theweight of the dispersion produced was 44.73 Kg containing 32.6% solids.The dispersion was coagulated with Nitric acid and dried at 170° C. Theraw dispersion particle size (RDPS) of the polymer particle was 0.296microns and the standard specific gravity was 2.156. The VDFconcentration in the copolymer was measured to be 3.48 mol % (2.26 wt%). The break strength of the beading was 6.6 lbs.

The matrix tensile strength of the specimen was measured to be 37,299psi.

EXAMPLE 2

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water,18 g of ammonium perfluoro-octanoic acid (APFO) and 5 g of succinic aciddissolved in about 50 g of DI water. The reactor and contents wereheated above the melting point of the wax. The reactor was repeatedlyevacuated and pressurized (to about 1 Atm or less) with TFE until theoxygen level was reduced to 20 ppm or less. The contents were brieflyagitated at about 60 rpm between evacuation and purge cycles to ensurethat the water was deoxygenated.

The reactor was heated to 83° C. and agitated at 60 rpm. Subsequently,0.8 MPa of trifluoroethylene (herein designated TrFE) was added followedby addition of TFE until the pressure reached 2.8 MPa. At this time,KMNO4 in a DI water solution (0.1 g/L) was injected at 80 mL/min untilapproximately 0.5 kg of TFE was consumed. At this time, the rate wasreduced to 40 mL/min until a second Kg of TFE was consumed. The pressurein the reactor was reduced to 50 Kpa using vacuum and pressurized withfresh TFE to 2.8 MPa. The KMnO4 was again added at 40 mL/min for thenext 0.5 Kg of TFE and continued until 4 Kg of TFE was consumed. After 4Kg of TFE was consumed, KMnO4 was no longer added.

Approximately 320 g of 20% APFO solution was added in 40 mL increments,the first increment being added after about 1 Kg of TFE had been added,followed by increments after each additional Kg of TFE, so that thefinal increment was added after 8 Kg of TFE had been reacted.

The polymerization reaction was then allowed to continue and thereaction stopped after 16 Kg of TFE had been added to the reactor. Theweight of the dispersion produced was 45.74 Kg containing 35.8% solids.The dispersion was coagulated with Nitric acid and dried at 170 C.

The raw dispersion particle size (RDPS) of the polymer particle was0.283 microns and the standard specific gravity was 2.213. Thetrifluoroethylene concentration in the copolymer was measured to be 3.2mol % (2.6 wt %). The break strength of the beading specimen was 7.24lbs.

The matrix tensile strength of the specimen was measured to be 28,602psi.

EXAMPLE 3

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water,18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic aciddissolved in about 50 g of DI water. The reactor and contents wereheated above the melting point of the wax. The reactor was repeatedlyevacuated and pressurized (to about 1 Atm or less) with TFE until theoxygen level was reduced to 20 ppm or less. The contents were brieflyagitated at about 60 rpm between evacuation and purge cycles to ensurethat the water was deoxygenated.

To the evacuated reactor, 8 mL of PFBE was charged, and the reactor washeated to 83° C. and agitated at 60 rpm. Subsequently, 0.8 MPa of VDFwas added followed by addition of TFE until the pressure reached 2.8MPa. At this time, KMNO4 in a DI water solution (0.1 g/L) was injectedat 80 mL/min until approximately 2 kg of TFE was added. After additionof the second Kg of TFE, the pressure in the reactor was reduced to 50Kpa using vacuum and pressurized with fresh TFE to 2.8 MPa. The KMnO4was added at 40 mL/min until the 4th Kg of TFE was consumed. After the4th Kg of TFE was added, KMnO4 was no longer added.

Approximately 320 g of 20% APFO solution was added in 40 mL increments,the first increment being added after about 1 Kg of TFE had been added,followed by increments after each additional Kg of TFE, so that thefinal increment was added after 8 Kg of TFE had been reacted.

The polymerization reaction was then allowed to continue and thereaction stopped after 16 Kg of TFE had been added to the reactor. Theweight of the dispersion produced was 42.76 Kg containing 29.0% solids.The dispersion was coagulated with Nitric acid and dried at 170° C.

The raw dispersion particle size (RDPS) of the polymer particle was0.263 microns and the standard specific gravity was 2.157. The VDFconcentration in the copolymer was measured to be 4.30 mol % (2.80 wt%). The PFBE concentration in the copolymer was measured to be 0.03 mol% (0.07 wt %), yielding a total copolymer concentration in thecomposition of 2.87 wt %. The break strength of the beading specimen was13.6 lbs.

The matrix tensile strength of the specimen was measured to be 44,878psi.

EXAMPLE 4

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water,18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic aciddissolved in about 50 g of DI water. The reactor and contents wereheated above the melting point of the wax. The reactor was repeatedlyevacuated and pressurized (to about 1 Atm or less) with TFE until theoxygen level was reduced to 20 ppm or less. The contents were brieflyagitated at about 60 rpm between evacuation and purge cycles to ensurethat the water was deoxygenated.

To the evacuated reactor, 19.94 g of PFOE was charged, and the reactorwas heated to 83 C and agitated at 60 rpm. Subsequently, 0.8 MPa of VDFwas added followed by addition of TFE until the pressure reached 2.8MPa. At this time, KMNO4 in a DI water solution (0.1 g/L) was injectedat 80 mL/min until approximately 2 kg of TFE was added. After additionof the second Kg of TFE, the pressure in the reactor was reduced to 50Kpa using vacuum and pressurized with fresh TFE to 2.8 MPa. The KMnO4was again added at 40 mL/min until an additional 0.5 Kg of TFE wasconsumed and reduced to 20 mL/min until 4 Kg of TFE was consumed. Afterthe 4th Kg of TFE was added, KMnO4 was no longer added.

Approximately 320 g of 20% APFO solution was added in 40 mL increments,the first increment being added after about 1 Kg of TFE had been added,followed by increments after each additional Kg of TFE, so that thefinal increment was added after 8 Kg of TFE had been reacted.

The polymerization reaction was then allowed to continue and thereaction stopped after 16 Kg of TFE had been added to the reactor. Theweight of the dispersion produced was 42.82 Kg containing 28.4% solids.The dispersion was coagulated with Nitric acid and dried at 170° C.

The raw dispersion particle size (RDPS) of the polymer particle was0.240 microns and the standard specific gravity was 2.159. The VDFconcentration in the copolymer was measured to be 3.50 mol % (2.20 wt%). The PFOE concentration in the copolymer was measured to be 0.03 mol% (0.16 wt %), yielding a total copolymer concentration in thecomposition of 2.36 wt %. The break strength of the beading specimen was14.1 lbs.

The matrix tensile strength of the specimen was measured to be 48,236psi.

EXAMPLE 5

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water,18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic aciddissolved in about 50 g of DI water. The reactor and contents wereheated above the melting point of the wax. The reactor was repeatedlyevacuated and pressurized (to about 1 Atm or less) with TFE until theoxygen level was reduced to 20 ppm or less. The contents were brieflyagitated at about 60 rpm between evacuation and purge cycles to ensurethat the water was deoxygenated.

To the evacuated reactor, 8 mL of PFBE were charged, and the reactor washeated to 83° C. and agitated at 60 rpm. Subsequently, TFE was addeduntil the pressure reached 2.8 MPa. At this time, KMnO4 in a DI watersolution (0.063 g/L) was injected at 80 mL/min until approximately 1 kgof TFE was added. At this time the pressure in the reactor was reducedto 50 Kpa using vacuum and pressurized with 0.8 MPa of VDF followed byaddition of TFE until the pressure reached 2.8 MPa. The KMnO4 was againadded at 80 mL/min until an additional 1 Kg of TFE was consumed at whichtime it was reduced to 40 mL/min until 4 Kg of TFE was consumed. Afterthe fourth Kg of TFE was consumed the pressure in the reactor wasreduced to 50 Kpa using vacuum and pressurized with fresh TFE to 2.8MPa. An additional amount of KMnO4 was added at 10 mL/min until thefifth Kg of TFE was consumed. After the consumption of the fifth Kg ofTFE, no more KMnO4 was added.

Approximately 320 g of 20% APFO solution was added in 40 mL increments,the first increment being added after about 1 Kg of TFE had been added,followed by increments after each additional Kg of TFE, so that thefinal increment was added after 8 Kg of TFE had been reacted.

The polymerization reaction was then allowed to continue and thereaction stopped after 16 Kg of TFE had been added to the reactor. Theweight of the dispersion produced was 48.8 Kg containing 34.5% solids.The dispersion was coagulated with Nitric acid and dried at 170° C.

The raw dispersion particle size (RDPS) of the polymer particle was0.234 microns and the standard specific gravity was 2.151. The VDFconcentration in the copolymer was measured to be 3.15 mol % (2.04 wt%), and the PFBE concentration in the copolymer was measured to be 0.03mol % (0.07 wt %), yielding a total copolymer concentration in thecomposition of 2.11 wt %. The break strength of the beading specimen was8.6 lbs.

The matrix tensile strength of the specimen was 10 measured to be 31,342psi.

EXAMPLE 6

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water,18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic aciddissolved in about 50 g of DI water. The reactor and contents wereheated above the melting point of the wax. The reactor was repeatedlyevacuated and pressurized (to about 1 Atm or less) with TFE until theoxygen level was reduced to 20 ppm or less. The contents were brieflyagitated at about 60 rpm between evacuation and purge cycles to ensurethat the water was deoxygenated.

The reactor was heated to 83° C. and agitated at 60 rpm. Subsequently,TFE was added until the pressure reached 2.8 MPa. At this time, KMnO4 ina DI water solution (0.063 g/L) was injected at 80 mL/min untilapproximately 1 kg of TFE was added. At this time the pressure in thereactor was reduced to 50 Kpa using vacuum and pressurized with 0.8 MPaof VDF followed by addition of TFE until the pressure reached 2.8 MPa.The KMnO4 was again added at 80 mL/min until an additional 2 Kg of TFEwas consumed at which time it was reduced to 40 mL/min until 4 Kg of TFEwas consumed. After the fourth Kg of TFE was consumed the pressure inthe reactor was reduced to 50 Kpa using vacuum and pressurized withfresh TFE to 2.8 MPa. An additional amount of KMnO4 was added at 40mL/min until the fifth Kg of TFE was consumed. After the consumption ofthe fifth Kg of TFE, no more KMnO4 was added.

Approximately 320 g of 20% APFO solution was added in 40 mL increments,the first increment being added after about 1 Kg of TFE had been added,followed by increments after each additional Kg of TFE, so that thefinal increment was added after 8 Kg of TFE had been reacted.

The polymerization reaction was then allowed to continue and thereaction stopped after 16 Kg of TFE had been added to the reactor. Theweight of the dispersion produced was 46.86 Kg containing 35.0% solids.The dispersion was coagulated with Nitric acid and dried at 170° C.

The raw dispersion particle size (RDPS) of the polymer particle was0.265 microns and the standard specific gravity was 2.158. The VDFconcentration in the copolymer was measured to be 3.35 mol % (2.17 wt%). The break strength of the beading specimen was 6.6 lbs. An SEM ofthe microstructure of the beading specimen is shown in FIG. 2.

The matrix tensile strength of the specimen was measured to be 26,053psi.

The copolymer material formed in this example was then blended withIsopar K (Exxon Mobil Corp., Fairfax, Va.) in the proportion of 0.196g/g of fine powder. The lubricated powder was compressed into a cylinderto form a pellet and placed into an oven set at 49° C. for approximately12 hours. The compressed and heated pellet was ram extruded to produce atape approximately 16.0 cm wide by 0.73 mm thick. The extruded tape wasthen rolled down between compression rolls to a thickness of 0.256 mm.The tape was then transversely stretched to approximately 56 cm wide(i.e., at a ratio of 3.5:1) and dried at a temperature of 250° C. Thedry tape was longitudinally expanded between banks of rolls over aheated plate set to a temperature of 345° C. The speed ratio between thesecond bank of rolls and the first bank of rolls was 10:1. The width ofthe expanded tape was 12.1 cm. The longitudinally expanded tape was thenexpanded transversely at a temperature of approximately 360° C. to aratio of approximately 25:1 and then constrained from shrinkage andheated in an oven set at 380° C. for approximately 24 seconds. An SEM ofthe resulting sheet is shown in FIG. 3, taken at 20,000× magnification,showing a node 1 and fibril 2 microstructure.

EXAMPLE 7

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water,18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic aciddissolved in about 50 g of DI water. The reactor and contents wereheated above the melting point of the wax. The reactor was repeatedlyevacuated and pressurized (to about 1 Atm or less) with TFE until theoxygen level was reduced to 20 ppm or less. The contents were brieflyagitated at about 60 rpm between evacuation and purge cycles to ensurethat the water was deoxygenated.

To the evacuated reactor, 8 mL of PFBE was charged, and the reactor washeated to 83° C. and agitated at 60 rpm. Subsequently, TFE was addeduntil the pressure reached 2.8 MPa. At this time, KMnO4 in a DI watersolution (0.063 g/L) was injected at 80 mL/min until approximately 1 kgof TFE was added. At this time the pressure in the reactor was reducedto 50 Kpa using vacuum and pressurized with 0.8 MPa of TrFE followed byaddition of TFE until the pressure reached 2.8 MPa. The KMnO4 was againadded at 80 mL/min until an additional 3 Kg of TFE was consumed. Afterthe fourth Kg of TFE was consumed the pressure in the reactor wasreduced to 50 Kpa using vacuum and pressurized with fresh TFE to 2.8MPa. An additional amount of KMnO4 was added at 40 mL/min until thefifth Kg of TFE was consumed. After the consumption of the fifth Kg ofTFE, no more KMnO4 was added.

Approximately 320 g of 20% APFO solution was added in 40 mL increments,the first increment being added after about 1 Kg of TFE had been added,followed by increments after each additional Kg of TFE, so that thefinal increment was added after 8 Kg of TFE had been reacted.

The polymerization reaction was then allowed to continue and thereaction stopped after 16 Kg of TFE had been added to the reactor. Theweight of the dispersion produced was 46.9 Kg containing 33.1% solids.The dispersion was coagulated with Nitric acid and dried at 170° C.

The raw dispersion particle size (RDPS) of the polymer particle was0.227 microns and the standard specific gravity was 2.217. The TrFEconcentration in the copolymer was measured to be 4.2 mol % (3.5 wt %),and the PFBE concentration in the copolymer was measured to be 0.03 mol% (0.07 wt %), yielding a total copolymer concentration in thecomposition of 3.57 wt %. The break strength of the beading specimen was3.48 lbs.

The matrix tensile strength of the specimen was measured to be 13,382psi.

EXAMPLE 8

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water,18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic aciddissolved in about 50 g of DI water. The reactor and contents wereheated above the melting point of the wax. The reactor was repeatedlyevacuated and pressurized (to about 1 Atm or less) with TFE until theoxygen level was reduced to 20 ppm or less. The contents were brieflyagitated at about 60 rpm between evacuation and purge cycles to ensurethat the water was deoxygenated.

The reactor was heated to 83° C. and agitated at 60 rpm. Subsequently,TFE was added until the pressure reached 2.8 MPa. At this time, KMnO4 ina DI water solution (0.063 g/L) was injected at 80 mL/min untilapproximately 1 kg of TFE was added. At this time the pressure in thereactor was reduced to 50 Kpa using vacuum and pressurized with 0.8 MPaof TrFE followed by addition of TFE until the pressure reached 2.8 MPa.The KMnO4 was again added at 80 mL/min until an additional 3 Kg of TFEwas consumed. After the fourth Kg of TFE was consumed the pressure inthe reactor was reduced to 50 Kpa using vacuum and pressurized withfresh TFE to 2.8 MPa. An additional amount of KMnO4 was added at 40mL/min until the fifth Kg of TFE was consumed. After the consumption ofthe fifth Kg of TFE, no more KMnO4 was added.

Approximately 320 g of 20% APFO solution was added in 40 mL increments,the first increment being added after about 1 Kg of TFE had been added,followed by increments after each additional Kg of TFE, so that thefinal increment was added after 8 Kg of TFE had been reacted.

The polymerization reaction was then allowed to continue and thereaction stopped after 16 Kg of TFE had been added to the reactor. Theweight of the dispersion produced was 4722 Kg containing 34.8% solids.The dispersion was coagulated with Nitric acid and dried at 170° C.

The raw dispersion particle size (RDPS) of the polymer particle was0.276 microns and the standard specific gravity was 2.219. The TrFEconcentration in the copolymer was measured to be 4.17 mol % (3.5 wt %).The break strength of the beading specimen was 3.95 lbs.

The matrix tensile strength of the specimen was measured to be 15,329psi.

EXAMPLE 9

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water,18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic aciddissolved in about 50 g of DI water. The reactor and contents wereheated above the melting point of the wax. The reactor was repeatedlyevacuated and pressurized (to about 1 Atm or less) with TFE until theoxygen level was reduced to 20 ppm or less. The contents were brieflyagitated at about 60 rpm between evacuation and purge cycles to ensurethat the water was deoxygenated.

The reactor was heated to 83° C. and agitated at 6 0 rpm. Subsequently,TFE was added until the pressure reached 2.8 MPa. At this time, KMnO4 ina DI water solution (0.063 g/L) was injected at 80 mL/min untilapproximately 1 kg of TFE was added. At this time the pressure in thereactor was reduced to 50 Kpa using vacuum and pressurized with 1.2 Kgof HFP followed by addition of TFE until the pressure reached 1.9 MPa.The KMnO4 was again added at 80 mL/min until an additional three Kg ofTFE was consumed. After the 4^(th) Kg of TFE was consumed the pressurein the reactor was reduced to 50 Kpa using vacuum and pressurized withfresh TFE to 2.8 MPa. An additional amount of KMnO4 was added at 80mL/min until the fifth Kg of TFE was consumed. After the consumption ofthe fifth Kg of TFE, no more KMnO4 was added.

Approximately 320 g of 20% APFO solution was added in 40 mL increments,the first increment being added after about 1 Kg of TFE had been added,followed by increments after each additional Kg of TFE, so that thefinal increment was added after 8 Kg of TFE had been reacted.

The polymerization reaction was then allowed to continue and thereaction stopped after 16 Kg of TFE had been added to the reactor. Theweight of the dispersion produced was 48.54 Kg containing 30.4% solids.The dispersion was coagulated with Nitric acid and dried at 170° C.

The raw dispersion particle size (RDPS) of the polymer particle was0.302 microns and the standard specific gravity was 2.157. The HFPconcentration in the copolymer was measured to be 0.77 mol % (1.25 wt%). The break strength of the beading specimen was 7.60 lbs.

The matrix tensile strength of the specimen was measured to be 34,178psi.

EXAMPLE 10

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water,18 g of ammonium perfluorooctanoic acid (APFO), 0.2 g FeSO4 and 5 g ofsuccinic acid dissolved in about 50 g of DI water. The reactor andcontents were heated above the melting point of the wax. The reactor wasrepeatedly evacuated and pressurized (to about 1 Atm or to less) withTFE until the oxygen level was reduced to 20 ppm or less. The contentswere briefly agitated at about 60 rpm between evacuation and purgecycles to ensure that the water was deoxygenated.

The reactor was heated to 83° C. and agitated at 60 rpm. Subsequently,0.81 MPa of CTFE was added followed by addition of TFE until thepressure reached 2.8 MPa. At this time, a solution containing 3 gammonium persulfate and 1 g sodium hydrosulfite in 2000 mL of DI waterwas injected at 40 mL/min until 2 Kg of TFE was consumed. After additionof the second Kg of TFE, the pressure in the reactor was reduced to 50Kpa using vacuum and pressurized with fresh TFE to 2.8 MPa. Additionalinitiator solution was again added at 20 mL/Min until a total of 2.5 Kgof TFE was consumed. At this time the rate was reduced to 10 mL/min.After 3 Kg of total TFE was consumed no more initiator was added.

Approximately 320 g of 20% APFO solution was added in 40 mL increments,the first increment being added after about 1 Kg of TFE had been added,followed by increments after each additional Kg of TFE, so that thefinal increment was added after 8 Kg of TFE had been reacted.

The polymerization reaction was then allowed to continue and thereaction stopped after 16 Kg of TFE had been added to the reactor. Theweight of the dispersion produced was 48.07 Kg containing 35.0% solids.The dispersion was coagulated with Nitric acid and dried at 170° C.

The raw dispersion particle size (RDPS) of the polymer particle was0.245 microns and the standard specific gravity was 2.228. The CTFEconcentration in the copolymer was measured to be 3.9 mol % (4.5 wt %).The break strength of the beading specimen was 7.6 lbs.

The matrix tensile strength of the specimen was measured to be 23,991psi.

Adhesion testing was performed, and the results are reported in Table 2.A DSC scan for this material is included in FIG. 4, which shows a firstmelt transition for the material at about 247° C.

EXAMPLE 11

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water,18 g of ammonium perfluorooctanoic acid (APFO), 0.2 g FeSO4 and 5 g ofsuccinic acid dissolved in about 50 g of DI water. The reactor andcontents were heated above the melting point of the wax. The reactor wasrepeatedly evacuated and pressurized (to about 1 Atm or less) with TFEuntil the oxygen level was reduced to 20 ppm or less. The contents werebriefly agitated at about 60 rpm between evacuation and purge cycles toensure that the water was deoxygenated.

To the evacuated reactor, 8 mL of PFBE was charged, and the reactor washeated to 83N C. and agitated at 60 rpm. Subsequently, 0.81 MPa of CTFEwas added followed by addition of TFE until the pressure reached 2.8MPa. A solution containing 3 g ammonium persulfate and 1 g sodiumhydrosulfite in 2000 mL of DI water was injected at 40 mL/min until 2 Kgof TFE were consumed. After addition of the second Kg of TFE, thepressure in the reactor was reduced to 50 KPa using vacuum andpressurized with fresh TFE to 2.8 MPa. Additional initiator solution wasagain added at 20 mL/Min until a total of 3.0 Kg of TFE was consumed.After the third Kg of TFE was consumed, no more initiator was added.

Approximately 320 g of 20% APFO solution was added in 40 mL increments,the first increment being added after about 1 Kg of TFE had been added,followed by increments after each additional Kg of TFE, so that thefinal increment was added after 8 kg of TFE had been reacted.

The polymerization reaction was then allowed to continue and thereaction stopped after 16 Kg of TFE had been added to the reactor. Theweight of the dispersion produced was 47.19 Kg containing 36.6% solids.The dispersion was coagulated with Nitric acid and dried at 170° C.

The raw dispersion particle size (RDPS) of the polymer particle was0.178 microns and the standard specific gravity was 2.247. The CTFEconcentration in the copolymer was measured to be 3.1 mol % (3.70 wt %)and the PFBE concentration in the polymer was measured to be 0.03 mol %(0.07 wt %), yielding a total copolymer concentration in the compositionof 3.77 wt %.

The break strength of the beading specimen was 3.48 lbs.

EXAMPLE 12

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water,18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic aciddissolved in about 50 g of DI water. The reactor and contents wereheated above the melting point of the wax.

The reactor was repeatedly evacuated and pressurized (to about 1 Atm orless) with TFE until the oxygen level was reduced to 20 ppm or less. Thecontents were briefly agitated at about 60 rpm between evacuation andpurge cycles to ensure that the water was deoxygenated.

The reactor was heated to 83° C., and agitated at 60 rpm. Subsequently,2.0 MPa of VDF was added followed by addition of TFE until the pressurereached 2.8 MPa. At this time, KMnO4 in a DI water solution (0.063 g/L)was injected at 80 mL/min until approximately 4 kg of TFE were added.The KMnO4 was added at 40 mL/min during addition of the next 2 kg ofTFE. After 6 Kg of TFE was consumed, no more KMnO4 was added.

Approximately 320 g of 20% APFO solution were added in 40 mL increments,the first increment being added after about 1 kg of TFE had been added,followed by increments after each additional Kg of TFE, so that thefinal increment was added after 8 kg of TFE had been reacted.

The polymerization reaction was then allowed to continue and thereaction stopped after 16 Kg of TFE had been added to the reactor. Theweight of the dispersion produced was 48.64 Kg containing 31.2% solids.The dispersion was coagulated with Nitric acid and dried at 170° C.

The raw dispersion particle size (RDPS) of the polymer particle was0.321 microns and the standard specific gravity was 2.137. The VDFconcentration in the copolymer was measured to be 11.8 mol % (7.90 wt%).

The break strength of the beading specimen was 10.53 lbs. The matrixtensile strength of the specimen was measured to be 37,000 psi.

Adhesion testing was performed, and the results are reported in Table 2.A DSC scan for this material is included in FIG. 4, which shows a firstmelt transition for the material at about 185° C.

EXAMPLE 13

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water,18 g of ammonium perfluorooctanoic acid (APFO), 1.5 g of ZnCl₂, and 5 gof succinic acid dissolved in about 50 g of DI water. The reactor andcontents were heated above the melting point of the wax. The reactor wasrepeatedly evacuated and pressurized (to about 1 Atm or less) with TFEuntil the oxygen level was reduced b 20 ppm or less. The contents werebriefly agitated at about 60 rpm between evacuation and purge cycles toensure that the water was deoxygenated.

The reactor was heated to 83° C. and agitated at 60 rpm. Subsequently,2.0 MPa of VDF was added followed by addition of TFE until the pressurereached 2.8 MPa. At this time, KMnO₄ in a DI water solution (0.1 g/L)was injected at 80 mL/min until was approximately 4 kg of TFE wereadded. The KMnO₄ was added at 40 mL/min during the next 2 Kg TFEaddition. After 5 Kg of TFE was consumed an additional 1 g of initiatorsolution was added. The total amount of KMnO₄ solution added was 3.375Kg.

Approximately 320 g of 20% APFO solution was added in 40 mL increments,the first increment being added after about 1 Kg of TFE had been added,followed by increments after each additional Kg of TFE, so that thefinal increment was added after 8 Kg of TFE had been reacted.

The polymerization reaction was then allowed to continue and thereaction stopped after 9 Kg of TFE had been added to the reactor. Theweight of the dispersion produced was 40.18 Kg containing 19.6% solids.The dispersion was coagulated with Nitric acid and dried at 170° C. Theraw dispersion particle size (RDPS) of the polymer particle was 0.339microns. The VDF concentration in the copolymer was measured to be 23.8mol % (16.7 wt %). The Break strength of the beading specimen was 8.62lbs. The matrix tensile strength of the specimen was measured to be23,511 psi.

Adhesion testing was performed, and the results are reported in Table 2.A DSC scan for this material is included in FIG. 4, which shows a firstmelt transition for the material at about 193° C.

A summary of the results given in the above Examples is provided inTable 1. Adhesion results are reported in Table 2. The foregoingexamples are provided to illustrate, without limitation, certainpreferred embodiments of copolymers produced according to the principlesdescribed herein. Additional copolymers, terpolymers, etc.,incorporating comonomers that are known to be reactive with TFE, canalso be used. These additional comonomers can be added in apredetermined concentration and allowed to react, with or withoutevacuation, based on the monomers' reactivity ratio to TFE, all of whichis known to one skilled in the art, as illustrated in the publishedliterature (see, e.g., Well-Architectured Fluoropolymers: Synthesis,Properties, and Applications; Elsevier; Amsterdam 2004, pp. 209).

While the invention has been disclosed herein in connection with certainembodiments and detailed descriptions, it will be clear to one skilledin the art that modifications or variations of such details can be madewithout deviating from the gist of this invention, and suchmodifications or variations are considered to be within the scope of theclaims hereinbelow.

TABLE 1 Particle Extrusion Extrudate Break Added size, pressure,strength, strength, MTS, Example comonomer(s) microns SSG psig psi lbspsi 1 VDF 0.296 2.156 3500 1046 10.40 37,299 2 TrFE 0.283 2.213 3501 9267.24 28,602 3 VDF/PFBE 0.263 2.157 3956 1139 13.60 44,878 4 VDF/PFOE0.240 2.159 4294 1257 14.10 48,236 5 VDF/PFBE 0.234 2.151 3434 944 8.6031,342 6 VDF 0.265 2.158 3123 862 6.60 26,053 7 TrFE/PFBE 0.227 2.2173522 963 3.48 13,382 8 TrFE 0.276 2.219 3085 847 3.95 15,329 9 HFP 0.3002.157 3350 988 7.60 34,178 10 CTFE 0.245 2.228 3640 953 7.60 23,991 11CTFE/PFBE 0.177 2.247 3817 1071 5.50 15,722 12 VDF 0.321 2.137 4110 104410.53 37,000 13 VDF 0.339 n/a 5680 1061 8.62 23,511

TABLE 2 Adhesion Adhesion Adhesion measure at measure at measure atMaterials 195° C. (J/m²) 290° C. (J/m²) 350° C. (J/m²) PTFE HomopolymerNo Adhesion No Adhesion 69.2 Example 10 No Adhesion 88.5 89.2 Example 1287.2 221 521 Example 13 15.3 105.3 383.5

What is claimed is:
 1. An expandable tetrafluoroethylene (TFE)copolymer, said copolymer containing 99.0% or less by weighttetrafluoroethylene monomer units and at least 1.0% by weight of atleast one other comonomer other than tetrafluoroethylene, wherein saidcopolymer exhibits adhesion.
 2. The expandable tetrafluoroethylene (TFE)copolymer of claim 1, wherein said adhesion is exhibited aftersubjecting the copolymer to a temperature at or below about 290° C. 3.The expandable tetrafluoroethylene (TFE) copolymer of claim 1, whereinsaid copolymer exhibits adhesion after subjecting the copolymer to itsfirst melt transition temperature or above.
 4. The expandabletetrafluoroethylene (TFE) copolymer of claim 1, wherein said copolymerexhibits adhesion after subjecting the copolymer to a temperaturebetween its first melt transition temperature and about 290° C.
 5. Thecopolymer of claim 1, wherein said at least one other comonomer is anolefin selected from the group consisting of ethylene, propylene andisobutylene.
 6. The copolymer of claim 1, wherein said at least oneother comonomer is a fluorinated monomer selected from the groupconsisting of chlorotrifluoroethylene (CTFE), hexafluoro-propylene(HFP), vinylidene fluoride (CFH═CH₂), vinylidene difluoride (CF₂═CH₂),hexafluoroisobutylene(HFIB), trifluoroethylene (CF₂═CFH), afluorodioxole and a fluorodioxalane.
 7. (canceled)
 8. (canceled)
 9. Thecopolymer of claim 1, wherein said at least one other comonomer is aperfluoroalkyl vinyl ether monomer.
 10. The copolymer of claim 9,wherein said perfluoroalkyl vinyl ether monomer is PMVE.
 11. Thecopolymer of claim 9, wherein said perfluoroalkyl vinyl ether monomer isPEVE.
 12. The copolymer of claim 9, wherein said perfluoroalkyl vinylether monomer is PPVE.
 13. The copolymer of claim 1, including more thanone other comonomer.
 14. The copolymer of claim 1, having at least 1.5%by weight polymerized units of at least one other comonomer.
 15. Thecopolymer of claim 1, having at least 2.0% by weight polymerized unitsof at least one other comonomer.
 16. The copolymer of claim 1, having atleast 3.0% by weight polymerized units of at least one other comonomer.17. The copolymer of claim 1, having at least 5.0% by weight polymerizedunits of at least one other comonomer.
 18. The copolymer of claim 1, inthe form of fine particles dispersed within an aqueous medium.
 19. Thecopolymer of claim 1, in the form of fine powder. 20-47. (canceled) 48.A medical device comprising the expandable tetrafluoroethylene (TFE)copolymer of claim 1, said copolymer containing 99.0% or less by weighttetrafluoroethylene monomer units and at least 1.0% by weight of atleast one other comonomer other than tetrafluoroethylene.
 49. Themedical device of claim 48 in the form of an implantable medical device.50. The medical device of claim 48 in the form of a vascular graft. 51.The medical device of claim 48 in the form of an endoluminal prosthesis.52. The medical device of claim 48, having a matrix tensile strength inat least one direction exceeding 13,000 psi.
 53. The medical device ofclaim 52 having a matrix tensile strength in at least one directionexceeding 15,000 psi.
 54. The medical device of claim 52 having a matrixtensile strength in at least one direction exceeding 25,000 psi.
 55. Themedical device of claim 52 having a matrix tensile strength in at leastone direction exceeding 30,000 psi.
 56. The medical device of claim 48in the form of an implantable medical device.
 57. The medical device ofclaim 48 in the form of a vascular graft.
 58. The medical device ofclaim 48 in the form of an endoluminal prosthesis.